1. Field of the Invention
This invention relates to an industrial truck for picking up a laterally disposed load from the ground or from racks, comprising at least one chassis beam, which extends transversely to the longitudinal direction of the truck and is provided on its parallel sides with guiding means for guiding a load carrier subassembly during its lateral displacement, which subassembly particularly comprises load carrier arms, which are movable beyond the contour of the industrial truck or of side beams and have fork arms which are connected by a crosspiece for guiding said arms on the guiding means, also comprising a feed drive for extending and retracting the load carrier and a lifting drive for vertically moving the load carrier relative to at least one chassis beam.
The reference to the picking up of a laterally disposed load involves the handling as such and includes also the deposition of a load.
The term load carrier subassembly generally describes a forked load carrier but does not exclude a load carrier subassembly which comprises a lifting frame, which is provided with a carriage that carries load carrier arms, which on an adjustable level are adapted to be extended into and to be retracted from shelves.
2. Description of the Prior Art
Industrial trucks of the kind described hereinbefore may be designed for an operation under the control of a driver but are preferably designed for an operation without a driver and in the latter case are guided and moved to register with locations on racks by means of guiding leads installed in the ground.
If a load carrier is to be laterally displaced for a picking up and deposition of loads when the truck is disposed in a narrow passage between racks, the crosspiece of the forked load carrier can be guided in known manner by guiding means comprising at least one roller and optional additional supports. Laterally extensible load carriers or fork arms are held freely and are not held in a defined elevation. There will be an elastic deformation particularly under a load.
From German Patent No. 12 83 152 it is also known to mount such load carriers on a laterally displaceable lifting frame, which is similarly guided and on which the load carrier can be extended by means of a scissors mechanism. In that case a downwardly extensible prop is provided to support the load carrier on the ground. Whereas such prop may be able to take up a certain lateral load, it will not facilitate the lateral movement of the load carrier and its movement under load. As the prop can be used only when the truck is at a standstill, its use will take considerable time. Moreover, such a prop will occupy a large space and requires that the load carrier when moving will be able to carry by itself a load.
German Patent Publication No. 10 19 969 discloses a side stacker provided with a load carriage on a lifting mast, which is displaceable transversely to the longitudinal axis of the truck. The entire lifting gear can be displaced on the level of the loading platform. In that case the structure may be relatively light in weight because a frame is provided which is continuous throughout the width of the truck and the lifting gear is moved as far as to the side edge of the truck approximately on the level of the loading platform. That design has been adopted to ensure that the frame of the truck has a high strength because the frame members are continuous. The expenditure is considerable because the telescopic lifting mast must be extensible also downwardly.
In accordance with German Patent Publication No. 10 19 968, actuating cylinders for imparting a transverse displacement to a lifting mast are rotatably mounted on lugs so that the drive means can be adapted to the movement throughout the transverse displacement of the lifting mast. In that design a horizontally movable carriage is provided with two rollers moving in a groovelike track. That feature also involves a considerable expenditure because in the known designs the fork arms are held and guided by the guiding means even when the arms are under load.
Austrian Patent Specification No. 254,770 discloses a frontally operating fork lift truck comprising a mast-base unit, which is movable up and down on the housing, and armlike feet disposed below said unit are provided with roller carriers, which are adapted to be raised and lowered by control rods. Those control rods are connected to a mechanism which during an up or down movement of the mast-base unit impart an axial displacement to the control rod so that load-carrying rollers will be extended. But such rollers are incorporated in the separate mast-base unit rather than on the load carrier. In that embodiment the forked load carrier has no load-supporting rollers and the loaded load carrier protrudes freely when it is under load.
It is an object of the design disclosed in Austrian Patent Specification No. 254,770 to provide a fork lift truck which has supporting legs and is as low as possible and has hollow forks, which can rest on the supporting legs. But that object can be accomplished only with restrictions when the fork arms of the load carrier are disposed over the mast-base unit and involves a considerable expenditure.